Techniques for the differentiation of carbon types present in lignite-rich mine soils

The objective of this study was to assess high energy UV photo-oxidation, 13C CP/MAS NMR spectroscopy and 14C activity measurements for their suitability in differentiating carbon derived from plant material and that derived from lignite. The conceptual approach included analysis of bulk soil samples and physical fractions of lignite-rich mine soils. Additionally, the <53 μm fraction of selected samples was subjected to 2 hours of high-energy UV photo-oxidation. Quantification of the lignite carbon content by 14C activity measurements showed that a mixture of lignite and recently formed organic matter occurs in the bulk surface soil horizon as well as a number of particle size and density fractions. Using 13C CP/MAS NMR spectroscopy, carbon species, characteristic for lignite- and plant-derived organic matter can be identified. Both methods yield corresponding results. It was also shown that lignite-derived carbon is more resistant to the high-energy UV photo-oxidation treatment than carbon derived from recent plant material. This method provides qualitative indications of lignite contribution to soils.